Sequential separation and recovery of phosphorus and lithium from lithium phosphate slag by selective extraction-precipitation

The efficient utilization of lithium and phosphate resources from lithium phosphate slag, a byproduct originated from lithium extraction, holds great significance for environmental protection and industrial advancement. Existing methods primarily focus on Li extraction from this slag, while phosphate resources are often overlooked. In this work, we proposed an alternative approach based on impurity extraction, followed by sequential precipitation of FePO4 and Li2CO3, to concurrently recover lithium and phosphate from lithium phosphate slag. The results demonstrated an aluminum separation efficiency of 85 %, effectively reducing the aluminum concentration in the raffinate to below 25.0 mg/L. The extraction reaction, facilitated by saponification, involved cation exchange between Al3+ and Na+. The synthesis process of FePO4·2H2O was predominantly controlled by the chemical reaction with an activation energy of 102.8 kJ/mol. The obtained FePO4·2H2O and Li2CO3 products met the standards for battery-grade materials. Notably, the process achieved a remarkable phosphorus recovery rate of 98.7 % while maintaining a low lithium loss rate of below 2.0 %. This work presents an efficient and environmentally friendly method for achieving comprehensive recovery of lithium and phosphate resources from lithium phosphate slag.